1. Field of the Invention
The present invention relates to a single-component diorganopolysiloxane composition exhibiting improved stability when it is stored in the absence of moisture, but which crosslinks at ambient temperature (typically 5.degree.-35.degree. C.) in the presence of water. A composition of this type is referred to below as a CVE composition (cold vulcanizable elastomeric composition).
The subject compositions are prepared principally by mixing hydroxylated diorganopolysiloxane polymers, fillers, particular polyalkoxylated silanes, organic or organosilicon amino compounds and metal or organometallic carboxylates or chelates.
2. Description of the Prior Art
Compositions prepared by mixing constituents which are closely related to those enumerated above are known to this art. Certain of these compositions are not stable when stored; they are, therefore, referred to as two-component compositions because of the fact that they must be packaged in two different packs with, for example, the hydroxylated diorganopolysiloxane polymers, the fillers and the alkoxylated silanes in one of the packs, and the amino compounds and the metal salts in the other pack.
This two-pack form is not very practical (especially for applications in building construction, which are quite frequently performed in the open air), in view of the facts that the contents of one of the packs have to be carefully mixed with the contents of the other only at the point in time of ultimate use and that all of the formed compositions must be used immediately.
Compositions of this type are described, in particular, in Belgian Pat. No. 774,830, and French Pat. Nos. 2,152,908 and 2,228,814.
Belgian Pat. No. 774,830 describes compositions prepared by mixing hydroxylated or alkoxylated diorganopolysiloxanes, alkoxylated silanes (or polysiloxanes), linear aminoalkylpolysiloxanes containing at least one aminoalkyl radical and at least one alkoxy radical, and curing catalysts.
French Pat. No. 2,152,908 describes compositions prepared by mixing hydroxylated diorganopolysiloxanes, alkoxylated silanes (or polysiloxanes), fillers, aminoorganosilanes containing hydrolyzable radicals and curing catalysts.
French Pat. No. 2,228,814 describes compositions prepared by mixing hydroxylated diorganopolysiloxanes, methylpolysiloxane resins, fillers, alkoxylated aminoorganosilanes (or aminoorganopolysiloxanes) and, if appropriate, alkyl silicates or polysilicates.
Other such compositions are stable when stored; they are referred to as single-component compositions and are packaged in a single pack.
Compositions of this latter type are disclosed, for example, in U.S. Pat. Nos. 3,161,614, 3,170,894 and 3,686,357 and in published Japanese Application No. 53/102,956.
U.S. Pat. Nos. 3,161,614 and 3,170,894 describe compositions prepared by mixing diorganopolysiloxanes blocked by a polyalkoxysiloxy unit at each end of their polymer chain and hardening catalysts, such as organic or organosilicon amines. These compositions are characterized by the presence of poorly accessible diorganopolysiloxanes principally obtained by the action of chloroalkoxysilanes on hydroxylated diorganopolysiloxanes; in addition, they set slowly when exposed to air, and this entails storing the assemblies bonded with the subject compositions, in workshops, for at least several days.
U.S. Pat. No. 3,686,357 describes compositions prepared by mixing diorganopolysiloxanes blocked by a polyalkoxysiloxy unit at each end of their polymer chain, linear aminoalkylpolysiloxanes, also blocked by a polyalkoxysiloxy unit at each end of their polymer chain, and hardening catalysts. These compositions are characterized by the presence of two kinds of polysiloxanes, the preparation of each of which requires a special processing step. Furthermore, their viscosity tends to increase during their storage. This increase in viscosity interferes to a considerable degree with their capacity for extrusion through the nozzles of the cartridges wherein they are typically packaged.
Japanese Application No. 53/102,956 describes compositions prepared by mixing organopolysiloxanes, each of which contains at least two silicon atoms bonded to alkoxy groups, crosslinking systems obtained by heating alkoxylated silanes (or polysiloxanes) with tin salts of carboxylic acids, and alkoxylated aminoorganosilanes. These compositions are characterized by the presence of, on the one hand, organopolysiloxanes which are not as accessible as the hydroxylated organopolysiloxanes and, on the other hand, crosslinking systems, the preparation of which requires a heating stage.
European Pat. No. EP-A-21,859 proposes a major step forward by way of a single-component CVE composition capable of being prepared in a single stage directly from the hydroxylated diorganopolysiloxane base polymers and from specific polyalkoxysilanes. According to this patent, the introduction of functional groups into the hydroxylated base polymer may be carried out by means of an organofunctional silane which also serves as the adhesion agent.
These single-component compositions may, however, exhibit inadequate storage stability.
According to recently published patent applications (EP-A-69,256, EP-A-104,179 and FR-A-2,543,562), this inadequate stability would appear to be due to the presence of residual silanols originating from the hydroxylated base polymer and which would not appear to be reacted with the polyalkoxysilanes.
Thus, European Patent Applications Nos. EP-A-69,256 and EP-A-104,179 and French Patent Application No. FR-A-2,543,562 suggest, with the goal of removing these residual silanols, the addition of a "scavenger" to the cold vulcanizable elastomeric composition which may be, respectively, a silane containing a labile hydrolyzable group which reacts preferentially with the residual silanol groups, a polysilazane and an organic compound containing at least one functional group which reacts with the silanol group.
As utilized hereinafter, by the term "stable", as applied to a single-component CVE composition containing an organopolysiloxane having alkoxy end groups according to the present invention, there is intended a mixture capable of setting when exposed to moisture, capable of remaining essentially unaltered when it is protected against atmospheric moisture, and which sets to an elastomer state which is not tacky to the touch even after an extended storage period. Furthermore, a "stable CVE composition" also connotes that the time which elapses to attain a nontacky state to the touch using the ingredients of a CVE composition which have been freshly mixed under atmospheric conditions will be essentially the same as that which elapses using the same mixture of ingredients subjected to atmospheric moisture after having been stored in a moisture-free and moisture-resistant container for an extended period of storage under ambient conditions, or an equivalent period based on accelerated aging at an elevated temperature.
After lengthy and expensive investigations, the present inventors have now established that the deterioration of the CVE compositions when stored appears to be principally due to the simultaneous presence in such CVE compositions of, on the one hand, the condensation catalyst based on a metal, especially tin, and, on the other hand, the catalyst for introducing functional groups into the hydroxylated oils, namely, a primary or secondary amine which catalyzes the reaction of the hydroxylated base polymer with the polyalkoxysilane, even when such catalyst is present in only very small amounts in the CVE composition.